There are two general types of rotary control valves: rotary concentric control valves, i.e., ball valves, and rotary eccentric control valves, i.e., plug valves. Both types of rotary control valves include a valve plug, having a plug head and plug body, that rotates toward and away from a valve seat. By covering and uncovering an orifice of the valve seat with the plug head of the valve plug, the rotary control valve is capable of controlling the flow of liquids and gases through the orifice. For a concentric or ball valve the shape of the valve plug is such that the plug head is centered with respect to a valve shaft which is centrally disposed about the centerline of the valve chamber. In contrast, an eccentric or plug valve positions the plug head such that it is offset relative to the valve shaft which itself is offset from the centerline of the valve chamber. Eccentric valves are designed so that the valve plug leaves contact with the seat immediately upon the start of opening.
It is known that the performance of a concentric valve degrades quickly due to the friction that occurs between the front surface of its plug head and the inner engaging surface of its valve seat. In particular, the plug head continually rubs against the valve seat during engagement and disengagement due to the concentric configuration of the valve plug and shaft. This rubbing action causes or tends to cause excessive wear to occur between the contacting surfaces of the valve plug and valve seat and, thus, increases leakage therebetween. In addition, this rubbing action causes the concentric valve assembly to apply a high amount of torque during the opening and closing of the concentric valve assembly as wear occurs.
In contrast, rotary eccentric control valve assemblies enable the plug head to pull away from the valve seat as it rotates in unison with the shaft. To accomplish this, eccentricity is built into the valve assembly. Conventional eccentric control valves accomplish this by building the eccentricity into the valve chamber and locating the spherical radius of the plug from the centerline of the valve chamber. This results in a functional design but large capital investments must be made to manufacture the product. Thus, eccentric valves do not suffer from the rubbing problem normally associated with concentric or ball valves. For example, U.S. Pat. No. 4,118,008, which issued on Oct. 3, 1978 to E. B. Myers, entitled ROTARY VALE, provides an eccentric plug assembly situated within a valve chamber having a plug head that is offset from a plug body. The plug head is offset from the valve body in order to compensate for the fact that the valve shaft about which the valve plug is disposed is itself offset from the centerline of the valve chamber. The displacement of the plug head and plug body enables the surface of the plug head to move away from an orifice of a valve seat at a steep angle. Thus, the plug head does not rub continually against the valve seat as it rotates within the valve chamber.
A rotary eccentric control valve having a plug body that is centered within the valve chamber is also known. For example, U.S. Pat. No. 3,379,408, which issued on Apr. 23, 1968 to W. E. Lowmy, entitled ECCENTRIC PLUG VALVE, provides an eccentric plug assembly having a plug head which is offset with respect to the valve shaft which is centrally disposed within the valve chamber. The problem with this patent is that the flow channel or orifice has also been offset with respect to the valve shaft so that the plug head is centrally disposed within the flow channel or orifice.
Another example is described in U.S. Pat. No. 2,803,426, which issued on Aug. 20, 1957 to D. De Zurik, entitled VALVES that provides a rotary plug assembly having a plug body disposed about a valve shaft that is centered within a valve chamber and a unique plug head which is centered (i.e., not offset) with respect to the valve shaft, but rather has different radius lengths at opposite ends of the plug head with respect to the valve shaft. This Patent also requires that one side of the valve seat be built up with respect to the other so as to accommodate the plug head having a decreasing thickness. Also, both of these patents describe immovable valve seats that are an integral part of the valve chamber. The valve seats are uniquely and unevenly formed within the valve chamber to accommodate the positions of the plug heads.
A vast majority of existing production machinery are designed to produce rotary concentric control valves that center the valve, shaft, valve plug and valve seat within the rotary concentric chamber. It would therefore be highly desirable if these readily available rotary concentric control valves could be modified to incorporate the non-rubbing benefits associated with eccentric control valves. There have been various attempts at modifying conventional rotary concentric control valves to incorporate the valve plug assemblies normally associated with rotary eccentric control valves, but these modifications typically require the removal of the centrally positioned valve shaft of the concentric control valve and replacing it with a new valve shaft which is offset from the centerline of the valve chamber and flow channel. This procedure is labor intensive and requires numerous new tooling, casting and molding for such modifications and, thus, is not economical for most situations. This has caused valve manufacturers to either cast completely new eccentric control valves or retrofit existing concentric control valves, as discussed above. Either of which is expensive and undesirable.
In order to overcome the above-mentioned disadvantages of the prior art, the present invention has uniquely created a hybrid rotary control valve which utilizes (a) the valve chamber of a conventional rotary concentric control valve having the valve shaft centrally disposed within its valve chamber, and (b) a valve plug having a plug head which is offset with respect to the valve shaft and flow channel such as the valve plugs used in conventional rotary eccentric control valves, thereby obtaining substantial cost savings over retrofitted concentric valves or newly cast rotary eccentric control valves. The present invention also has a removable and replaceable dynamic valve seat that may be situated within an existing conventional rotary concentric valve chamber which can be manufactured by existing production machinery and yet adapt and compensate for the offset position of the plug head to form a leak-tight fit between the valve seat and the plug head. It is also desirable that the hybrid rotary control valve of the present invention provides a multitude of flow characteristics without adding to manufacturing and product cost.
Use of a dynamic orbital valve seat dramatically reduces the torque required to shutoff the valve. The torque reduction has a positive impact on reducing valve cost. The shaft size of the valve can be reduced as well as the size of the valve plug. These items are typically high alloy materials which are expensive to purchase. By down sizing these components, less material is used resulting in cost savings. Another benefit of the lower torque is that smaller actuators can be used to actuate the valve. This also results in substantial cost savings.
The valve torque reduction allows the use of a two piece shaft design, i.e., an upper splined end and a lower end of a shaft. Typically, existing rotary eccentric control valves use a one piece shaft that extends through the valve chamber since such a shaft is necessary to carry high torque loads. Such a one piece shaft protrudes into the flow passage of the valve chamber and reduces flow capacity. The two piece shaft does not protrude into the flow passage resulting in a 50% or greater increase in flow capacity of the hybrid rotary control valve.